Immunological evidence for the synthesis of all canine distemper virus polypeptides in chronic neurological diseases in dogs. Chronic distemper and old dog encephalitis differ from SSPE in man

Experimental old dog encephalitis (ODE) in a gnotobiotic dog

Experimental infection of a gnotobiotic Beagle dog with the neurovirulent R252 strain of canine distemper virus (R252-CDV) resulted in long-term central nervous system (CNS) infection; cerebral and brain stem lesions were consistent with old dog encephalitis (ODE). Eight clinical cycles of relapsing cortical and subcortical signs were documented over 33 months and were corroborated by the presence of both chronic and active inflammatory demyelinating lesions within the neuraxis. Immunocytochemistry revealed that CDV antigen was restricted to neurons. Attempts to use fresh brain tissue to directly transmit the infection to CDV-susceptible gnotobiotic dogs were unsuccessful. Reisolation of infectious virus from the infected dog required prolonged culture and coculture of brain explant cells with CDV-susceptible Vero cell monolayers. These findings demonstrate that ODE is a variant of virulent CDV-induced canine neurologic disease that can evolve de novo within the CNS of subclinically infected dogs in the absence of external sources of reinfection. The highly cell-associated nature of the virus, when first recovered from this dog, suggests that the virus was present within the CNS in a replication-defective form.

Comparative antibody response in harbour and grey seals naturally infected by a morbillivirus

The antibody response of free-ranging harbour and grey seals, naturally infected by a morbillivirus, was assessed using a virus neutralizing test and a radio-immunoprecipitation assay. The prevalence of antibody was similar between species, however, grey seals had significantly higher virus neutralizing titers. Serum from clinically healthy grey seals precipitated the nucleocapsid (N) protein along with the hemagglutinin (H) and fusion (F) glycoproteins. By contrast, significantly fewer harbour seal sera precipitated the envelope glycoproteins and responses were weaker than those of grey seals. One harbour seal with acute morbillivirus pneumonia, and two with encephalitis precipitated only the N protein. Serum from four harbour seals with encephalitis weakly recognized the envelope glycoproteins. Thus, the antibody response of grey seals appears more competent than that of harbour seals with respect to morbillivirus antigens. We speculate that this difference between the species may be an important determinant of morbillivirus susceptibility.

Correlation between humoral immune responses and presence of virus in the CNS in dogs experimentally infected with canine distemper virus

The role of the humoral immune response in clearance or prevention of canine distemper viral encephalitis of dogs infected with a virulent strain of canine distemper virus has been evaluated. Dogs that have demyelinating lesions, CDV proteins and infectious virus in their brains demonstrate an impaired humoral immune response. In dogs that recover from infection and contain no demyelinating lesions, viral proteins or infectious virus in the brain, antibodies to the internal proteins of CDV are observed early after infection. Later antibodies to primarily the H protein are detectable in sera of these dogs and the appearance of antibodies against the surface glycoprotein (H) correlates with the absence of lesions, CDV antigen and infectious virus in the brains of these dogs. Very late after infection immunoprecipitating antibody to all CDV antigens diminished rapidly so that at about ten weeks post infection antibodies that precipitate CDV antigens are barely detectable.

Viral expression in experimental canine distemper demyelinating encephalitis

We have characterized the relationship between the expression of canine distemper virus (CDV) and demyelinating lesions in the white matter of the cerebellum of experimentally infected dogs. In animals which had demyelinating lesions, CDV proteins (N, P, F and H) were expressed and infectious virus could be recovered from brain tissue. Viral proteins (N, P, F and H) were detected by monoclonal antibodies and immunocytochemistry within demyelinating lesions as well as in scattered glial cells in areas of the white matter which lacked detectable lesions. Many cell types, including astrocytes, neurons, ependymal cells, choroid plexus cells, meningeal cells and perivascular inflammatory cells were labelled for viral antigen. We conclude from our results that the mechanism of demyelination in canine distemper virus-induced encephalitis involves expression of viral gene products at the lesion site.

Naturally occurring canine distemper virus encephalitis: distribution and expression of viral polypeptides in nervous tissues

Formalin-fixed brain tissues from 16 dogs with naturally occurring canine distemper virus (CDV) infection were investigated immunohistochemically by a panel of eight monoclonal antibodies (mAb) directed against four structural CDV proteins. Three mAb recognizing different epitopes of the polymerase (P-1, P-2, P-3) protein, two clones identifying different epitopes on each, the nucleocapsid (NP-1, NP-2) and fusion (F-2, F-3) protein, and one mAb directed against the hemagglutinin (H-2) protein were used. The immunoreactivity of the clones was tested on formalin-fixed, paraffin-embedded Vero cells, which were lytically infected with the neurotropic R252 (R252-CDV) or the Onderstepoort (CDV/Ond) strain of CDV. Clones directed against the H-2 and F-3 epitope recognized CDV/Ond but not R252-CDV. The remaining six clones showed positive immunoreaction with both CDV strains. In vivo expression and distribution of the individual proteins and their epitopes varied substantially between animals and within lesions from the same animal. The NP-2 epitope showed positive immunostaining in all 16 cases. The P-2 epitope was demonstrated in 13, the NP-1 epitope in 12, the P-3 epitope in 9, and the P-1 epitope in 3 brains, but staining was severely reduced compared with the NP-2 epitope and restricted to areas with strong NP-2 expression. Immunostaining was prominent in early and subacute and reduced in chronic demyelinating lesions. mAb directed against the H and F protein showed no immunoreaction in diseased brains.

Production of immunoglobulin G and increased antiviral antibody in cerebrospinal fluid of dogs with delayed-onset canine distemper viral encephalitis

Sera and cerebrospinal fluid (CSF) from four dogs with delayed-onset canine distemper viral (CDV) encephalitis (old dog encephalitis) were compared with samples from dogs with acute CDV and from recently vaccinated controls. Dogs with old dog encephalitis (ODE) had elevated CSF IgG concentrations (122 micrograms/ml) compared to controls (13 micrograms/ml) without elevated CSF albumin; their CSF IgG index was significantly greater. CSF proteins banding in the alkaline region of isoelectric focusing gels were immunochemically identified as IgG. Detectable viral neutralizing antibody was present in ODE CSF, and formed a larger proportion of IgG in CSF than in serum. Serum samples containing 2 mg IgG bound to all viral polypeptides of both R252 and Onderstepoort CDV isolates by immunoblot analysis. CSF samples of ODE patients bound viral antigens when diluted to contain as little as 5-40 micrograms IgG, while patient serum could be diluted to 40-200 micrograms IgG content compared to serum IgG of 100 micrograms/ml in vaccinated controls. Serial CSF dilutions consistently bound to H and NP polypeptides at the highest dilutions, similar to the binding of serums from recently vaccinated dogs. Thus, dogs with delayed-onset CDV encephalitis have elevated concentrations of CSF IgG, much of which is virus-specific, with an antigen binding pattern similar to that of sera of recently immunized dogs.

Autologous and allogeneic antibody responses to canine distemper virus isolates from dogs with chronic neurological diseases

We describe the antibody responses to three strains of canine distemper virus (CDV) isolated from dogs with chronic neurological disease in the Los Angeles area using the naturally occurring sera and cerebrospinal fluids (CSFs) of these animals as probes for comparison. CDV/CDE-2 was derived from a dog with chronic distemper encephalitis, and CDV/ODE-8 and CDV/ODE-10 were derived from dogs with old dog encephalitis. Sera and CSFs were used in autologous (same dog) and allogeneic (different dog) combinations to immune precipitate the [35S]-methionine-labelled H, P, NP, F1, and M polypeptides of the virus-infected cell cultures. The polypeptides were separated by SDS-PAGE and detected by fluorography. There was decreased recognition by the CSF and sera of the polypeptides of the viral isolates in several autologous as well as allogeneic combinations. It is concluded that the immune responses to the CDV strains are not identical, and it is likely that viral mutations occurred after the animals were infected. Some mutations may have contributed to the pathogenesis of distemper encephalitis in these animals and some may have occurred during subsequent passage of the viruses in cell culture. This may explain the decreased recognition of the polypeptides of the viral isolates by the CSF and sera.

Canine distemper virus clearance in chronic inflammatory demyelination

The distribution of canine distemper virus (CDV) antigen was examined in the brains of 14 dogs with chronic nervous distemper using a monoclonal antibody against a major viral protein. In ten of these dogs, neutralizing anti-CDV antibody titers were determined in serum and unconcentrated cerebrospinal fluid (CSF). In 19% of the inflammatory demyelinating lesions, large amounts of CDV antigen were found; in 34% of these lesions only residual traces of virus were seen and in almost half of the lesions (47%) no CDV could be demonstrated. In four dogs neutralizing antibodies were found in the serum only; in one dog in the CSF only and in 5 dogs both in serum and CSF. Because of the correlation between the presence of inflammation, intrathecal antiviral antibodies and disappearance of CDV from the lesions, it was concluded that the inflammatory response in distemper is associated with viral clearance from the lesions. Associated immune-mediated cytotoxic reactions could explain exacerbation of the initial virus-induced demyelinating lesions. Despite the presence of an apparently effective intrathecal antiviral immune response, fresh non-inflammatory lesions as a result of viral replication and spread in the white matter coexisted with inflammatory ones in which viral clearance had taken place. The role and mechanism of such virus persistence are discussed.

Development of antibody to measles virus polypeptides during complicated and uncomplicated measles virus infections

Immune precipitation of 181 sera from 152 patients with natural measles was studied to determine the temporal course and frequency of antibody responses to nucleocapsid, fusion, hemagglutinin, and matrix proteins of measles virus. Large amounts of antibody to nucleocapsid protein developed in all patients by day one of the rash. Antibody to hemagglutinin and fusion proteins developed in all patients over the next 3 weeks, the former to high levels and the latter to low levels. Antibody to matrix protein developed to very low levels and was detectable in only 41% of the patients; this poor response to matrix protein was not correlated with the age of the patient or the acute neurological complications of measles.

Canine distemper encephalomyelitis: variation with virus strain

Disease induced by 3 virulent strains of Canine Distemper Virus (CDV) was compared in specific pathogen-free Beagle dogs. All strains produced an encephalomyelitis but variation was observed in the severity, clinical course and resulting neuropathology. Infection with Snyder Hill strain of CDV was consistently acute; dogs either succumbed 14 to 19 days post-inoculation (PI) or recovered. Lesions in the neuraxis were those of a polioencephalomyelitis. In contrast, CDV strain A75-17 produced subacute to chronic disease in which demyelination was the predominant finding. Some dogs succumbed, generally around 28 to 42 days PI. Total recovery was again recorded for some members of the group. Others developed persistent central nervous system (CNS) infection but remained clinically stable until electively killed with barbiturate, up to 62 days PI. CDV strain R252 also induced delayed, predominantly white matter disease with a mixed pattern of mortalities, persistent infections and recoveries, similar to A75-17. Neutralizing antibody responses correlated with the disease course. Dogs which died had low serum titres or lacked serum antibody. Recovering dogs had the earliest and highest titres. A few dogs with persistent CNS infection had antibody in the cerebrospinal fluid also. Current concepts of the pathogenesis of canine distemper encephalomyelitis (CDE) are discussed and a basis for the strain-dependent clinical and pathological expression of CDE is proposed. Viral strain appears to be an important factor in this common disease of the canine CNS.

Does virus persist in the uvea in multiple sclerosis, as in canine distemper encephalomyelitis?

Epidemiological studies suggest that multiple sclerosis (MS) might be triggered by an infectious agent. Uveitis has been observed in a small percentage of MS patients. Dogs with canine distemper encephalomyelitis, another demyelinating disease of the central nervous system, have an anterior uveitis which is usually mild and asymptomatic, and dogs with persistent CNS infection and chronic distemper encephalomyelitis harbour virus persistently in the uvea. These observations in dogs suggest that pathological and virological studies of the uveitis associated with MS would be worth while.

Antibody responses to virion polypeptides in gnotobiotic dogs infected with canine distemper virus

A radioimmunoprecipitation-polyacrylamide gel electrophoresis technique was applied to sera from canine distemper virus-infected dogs. Sera from fatally infected dogs precipitated only the nucleoprotein, the matrix protein, and trace amounts of fusion glycoprotein. Sera from normal convalescent dogs precipitated all five major polypeptides. In contrast, sera from persistently infected dogs were characterized by a modest overall response compared with sera from convalescent dogs and by no or little response to the matrix and phosphorylated proteins until 5 to 7 weeks after infection.